Magnetron



July 12, 1938. H. E. HOLLMANN MAGNETRON Filed Nov. 27, 1936 INVENTORHANS ERICH HOLLMANN fi ATTO R N EY Patented July 12, 1938 UNITED STATESPATENT OFFICE MAGNETRON ration of Germany Application November 27, 1936,Serial No. 112,977

' In Germany November 29, 1935 1 Claim.

My invention relates to electron discharge devices, more particularly toimprovements in socalled magnetrons in which the electrode system ispositioned in a magnetic field.

Investigations regarding the oscillation mechanism of magnetrons haveshown that in a magnetron tube whose anode cylinder is divided by two ormore slots into two or more segments, two different forms ofoscillations of ultra short waves appear, in accordance with the chosenoperating conditions, i. e. plate potential and strength of the magneticfield, and in accordance with the tuning of the outer resonance circuitsconnected to the segments. In one form of oscillation there is to bedealt with rotations of space charges produced by the action of theelectrical field and the magnetic field extending at right angle to eachother. This form of oscillation is not only attainable in a split anodemagnetron, but also in a solid anode cylinder magnetron, and extends inthe present state of the art downwards to waves of about one centimeter.The other type of oscillation has its actual origin in a negativeelectron resistance produced between the plate segments, and whichexcites the oscillatory system connected with the segments. Theproduction of such negative electron resistance is to be found in thescrew shaped course of the electron movement, such as result from theaction of the radial and tangential electrical fields in the vicinity ofthe separation gaps of the segments in conjunction with the magneticfield extending substantially in the axial direction. This form ofoscillation although not attaining the aforementioned high frequencyowing to the natural inertia of the electron movement, produces howeverat 2 to 4 times longer waves a very much higher useful energy and a muchmore favorable eiiiciency.

The object of my invention is to provide an electrode arrangement andconnection for a magnetron for increasing its efficiency.

To increase the efficiency and use of the energy of a magnetron I dividethe plate cylinder into several segments, and so combine the segmentsthat the negative electron resistances existing between the separatinggaps of the segments, operate in parallel. However this can apparentlyonly be assured when the high frequency potentials at all adjacentsegment edges are of opposite phase. In order to secure this optimumstate of oscillation of the segments, in the hitherto used structures ofmagnetron transmitters the segments situated diametrically opposite eachother are connected together in pairs by means of one or several bentwire straps reaching around the plate cylinder. In a four part anode,two pairs of segments are obtained in this way each of which isconnected to a pole of the resonance circuit to be excited.

When arriving at increasingly shorter waves, the natural frequencies ofthe small resonance circuits in the tube proper, and which are formed bythe mutual capacity of the opposite segments, and the induction of thecorresponding closing bend or connecting conductors, cause considerabledisturbance, the more so since the connecting conductors when reachingat the outside around the anode cylinder must have a definite minimumlength. Waves that are shorter than those which correspond to thosesmall resonance systems thus either cannot be produced at all with sucha tube, or only at a very poor useful effect.

Another drawback of these hitherto ordinary constructions of the anodesegment system is to be seen in the fact that for instance with a foursplit anode, segments arranged diametrically opposite to each other haveopposite high frequency potentials. This signifies however, that twoadjacent segments have equal alternating potentials, and that the splitportions situated between them cannot participate in the production ofoscillations. I Only the edges of the segments on both sides of theother two split portions actually carry opposite potentials and theyalone must effect the excitation. Thus the tube is only unilaterallyexploited and in an entirely incomplete manner.

By means of the arrangement of the connecting conductors described inthe present invention, these drawbacks, namely the excessive length ofthe conductors as well as the various inclusions of the existingnegative electron resistances in the building-up mechanism are safelyeliminated. To this end, the invention is based upon the principlejoining two adjacent segments by means of connection straps instead ofconnecting segments situated diametrically opposite to each other.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claim, but theinvention itself will best be understood by reference to the followingdescription taken in connection with the accompanying drawing in whichFigure 1 is a diagrammatic transverse section of an electron dischargedevice embodying my invention, Figure 2 shows a detail of construction,and Figure 3 is a perspective of the mount shown in Figure 1 with a partbroken away to show details of construction.

All of the four segments S1 to S4 around cathode C are connected witheach other by four conductors B1 to B4, whereby these conductors act, aspreviously, as inductances, and form small resonance systems with themutual capacities of the segments. Electrode elements are mounted withinan envelope E surrounded by the coil M for inducing a. magnetic fieldparallel to the electrode elements within the envelope. Now whenconsidering the incidental values of the high frequency potentialsdistributed over the segments, it can be seen that in fact all adjacentsegments must oscillate in opposite phase, since at the ends of thebent straps or conductors, only voltages having opposite phase canappear when said ends oscillate in their natural frequency. Whenconsidering the electrode assembly, and hence also the state ofoscillation as being completely symmetrical, oscillation anodes will beproduced on all four culmination points k of the conductors. This means,that the inductance of the two adjacent conductor branches up to theculmination points, is to' be considered as being placed in parallel tothe inductance of each individual strap or conductor.

The arrangement must obviously not necessarily be such that, asindicated in the figure, the points at which the two connections meetthe segment, coincide, the points may also be apart from each other, forinstance moved towards the edges of the segments. Furthermore, ifespecially high frequencies are to be produced, it may eventually be ofadvantage, instead of passing the straps along the outside of the platecylinder, to arrange them in the extended outer cylindrical surface inwhich the anodes are situated, and where they can be maintained muchshorter. Such bent connections-may also be arranged on both sides of theplate cylinder or segments.

'In accordance with a further proposition, in place of the wire straps,sheet metal strips may be used to advantage, having the same width asthe length of the-electrode system for instance. The cross sectionthrough such a rosette shaped system remains thereby unchanged asindicated in the figure. The technical construction is especially simpleif each strap forms a single piece withthe two halves of the adjacentsegments, and if the piece is riveted or welded at the bent edges, tothe straps on both sides. Such structural part consisting of a strap andtwo segment halves thus has the cross section shown in Figure 2, and isjoined to the following part at the edges a. Such sheet metal strips notonly have the advantage of very low damping losses, but assurefurthermore a uniform state of oscillation of the segments, and preventundesirable longitudinal oscillations while assuring at the same time afavorable heat delivery, and high load capacity of the tubes.

In order to still further enhance the heat delivery, the straps may beformed as hollow bodies and have a suitable cooling means flow throughthem. Since the entire system is closed in itself, the cooling fluid maybe suitably introduced for instance at the lower culmination point (seeFigure 1) from where it will be branched towards the right and the left,and caused to leave at the upper culmination point. The principle of theconstruction of the segment set in accordance with the invention andrelating to the high frequency part has no influence upon the otherstructures of the generator dealing with measures known as such, as forinstance end plates maintained at suitable potential, or severalfilaments.

While I have indicated the preferred embodiments of my invention ofwhich I am now aware and have also indicated only one specificapplication for which my invention may be employed, it will be apparentthat my invention is by no means limited to the exact forms illustratedor the use indicated, but. that many variations may be made in theparticular structure used and the purpose for which it is employedwithout departing from the scope of my invention as set forth in theappended claim.

What I claim as new is:

An electron discharge device having a straight cathode, a plurality ofpairs of sheet metal anode segments coextensive with each other andsurrounding said cathode, conductors connecting adjacent anode segments,said conductors comprising sheet metal straps equal in width to thelength of said anode segments, and means for producing a magnetic fieldparallel to said cathode.

HANS ERICH HOLLMANN.

